The treatment of tumors by hyperthermia is known. In one known process, tumors and other lesions to be treated can be heated above a predetermined temperature of the order of 55 C so as to coagulate the portion of tissue heated. The temperature range is preferably of the order of 55 to 65 C and does not reach temperatures that can cause carbonization or ablation of the tissue.
One technique for effecting the heating is to insert into the lesion concerned an optical fiber, which has at its inserted end an element that redirects laser light from an exterior source in a direction generally at right angles to the length of the fiber. The energy from the laser thus extends into the tissue surrounding the end or tip and effects heating. The energy is directed in a beam confined to a relatively shallow angle so that, as the fiber is rotated, the beam also rotates around the axis of the fiber to effect heating of different parts of the lesion at positions around the fiber. The fiber can thus be moved longitudinally and rotated to effect heating of the lesion over the full volume of the lesion with the intention of heating the lesion to the required temperature without significantly affecting tissue surrounding the lesion. We define the term “lesion” as used herein to mean any pathologic change in the tissue or organs of a mammalian subject including, but not limited to, tumors, aortic or other aneurysms, artery and vein malformations such as thrombosis, hemorrhages, and embolisms.
At this time the fiber is controlled and manipulated by a surgeon with little or no guidance apart from the knowledge of the surgeon of the anatomy of the patient and the location of the lesion. It is difficult therefore for the surgeon to effect a controlled heating which heats the entire lesion while minimizing damage to surrounding tissue.
It is of course well known that the location of tumors and other lesions to be excised can be determined by imaging using a magnetic resonance imaging system. The imaging system thus generates for the surgeon a location of the lesion to be excised but there is no system available which allows the surgeon to use the imaging system to control the heating effect. In most cases it is necessary to remove the patient from the imaging system before the treatment commences and that movement together with the partial excision or coagulation of some of the tissue can significantly change the location of the lesion to be excised thus eliminating any possibility for controlled accuracy.
It is also known that magnetic resonance imaging systems can be used by modification of the imaging sequences to determine the temperature of tissue within the image and to determine changes in that temperature over time.
U.S. Pat. No. 4,914,608 (LeBiahan) assigned to U.S. Department of Health and Human Services issued Apr. 3, 1990 discloses a method for determining temperature in tissue.
U.S. Pat. No. 5,284,144 (Delannoy) also assigned to U.S. Department of Health and Human Services and issued Feb. 8, 1994 discloses an apparatus for hyperthermia treatment of cancer in which an external non-invasive heating system is mounted within the coil of a magnetic resonance imaging system. The disclosure is speculative and relates to initial experimentation concerning the viability of MRI measurement of temperature in conjunction with an external heating system. The disclosure of the patent has not led to a commercially viable hyperthermic treatment system.
U.S. Pat. Nos. 5,368,031 and 5,291,890 assigned to General Electric relate to an MRI controlled heating system in which a point source of heat generates a predetermined heat distribution which is then monitored to ensure that the actual heat distribution follows the predicted heat distribution to obtain an overall heating of the area to be heated. Again this patented arrangement has not led to a commercially viable hyperthermia surgical system.
An earlier U.S. Pat. No. 4,671,254 (Fair) assigned to Memorial Hospital for Cancer and Allied Diseases and issued Jun. 9, 1987 discloses a method for a non surgical treatment of tumors in which the tumor is subjected to shock waves. This does not use a monitoring system to monitor and control the effect.
U.S. Pat. No. 5,823,941 (Shaunnessey) not assigned issued Oct. 20, 1998 discloses a specially modified endoscope which designed to support an optical fiber which emits light energy and is moved longitudinally and rotates angularly about its axis to direct the energy. The device is used for excising tumors and the energy is arranged to be sufficient to effect vaporization of the tissue to be excised with the gas thus formed being removed by suction through the endoscope. An image of the tumor is obtained by MRI and this is used to program a path of movement of the fiber to be taken during the operation. There is no feedback during the procedure to control the movement and the operation is wholly dependent upon the initial analysis. This arrangement has not achieved commercial or medical success.
U.S. Pat. No. 5,454,807 (Lennox) assigned to Boston Scientific Corporation issued Oct. 3, 1995 discloses a device for use in irradiating a tumor with light energy from an optical fiber in which in conjunction with a cooling fluid which is supplied through a conduit with the fiber to apply surface cooling and prevent surface damage while allowing increased levels of energy to be applied to deeper tissues. This arrangement however provides no feedback control of the heating effect.
U.S. Pat. No. 5,785,704 (Bille) assigned to MRC Systems GmbH issued Jul. 28, 1996 discloses a particular arrangement of laser beam and lens for use in irradiation of brain tumors but does not disclose methods of feedback control of the energy. This arrangement uses high speed pulsed laser energy for a photo-disruption effect.
Kahn, et al. in Journal of Computer Assisted Tomography 18 (4):519-532, July/August 1994; Kahn, et al. in Journal of Magnetic Resonance Imaging 8: 160-164, 1998; and Vogl, et al. in Radiology 209: 381-385, 1998 all disclose a method of application of heat energy from a laser through a fiber to a tumor where the temperature at the periphery of the tumor is monitored during the application of the energy by MRI. However none of these papers describes an arrangement in which the energy is controlled by feedback from the monitoring arrangement. The paper of Vogl also discloses a cooling system supplied commercially by Somatex of Berlin Germany for cooling the tissues at the probe end. The system is formed by an inner tube through which the fiber passes mounted within an outer tube arrangement in which cooling fluid is passed between the two tubes and inside the inner tube in a continuous stream.